The subject matter disclosed herein relates to a circuit breaker having a current transformer.
Circuit breakers are widely used to protect electrical lines and equipment. The circuit breaker monitors current through an electrical conductor and “trips” to open the electrical circuit and thus interrupt current flow through the circuit provided that certain predetermined criteria are met, such as an over-current condition. An electronic trip unit (“ETU”) is a device that is used in conjunction with a circuit breaker to control the current (and/or voltage) versus time trip response. The ETU is a programmable device which measures and times current flowing through the circuit breaker and initiates a trip signal when appropriate. The circuit breaker includes circuits that measure current in the device. Current-sensing transformers sense circuit current and provide current signals to the ETU for processing. Current transformers and Rogowski coils monitor the current in the circuit breaker. The current transformer is used for powering the ETU without use of external auxiliary power. The current transformer provides current output to the ETU that is proportional to the primary current flowing through it. Heat is developed due to current transformer losses. Rogowski coil is used for saturation free measurement of current in the conductor of the circuit breaker. Rogowski coil provides a voltage output that is proportional to the time derivative of the current, rather than a current output like traditional current transformers. To withstand certain impulse tests, insulating tape is pasted on the load terminal.